Applications of Thermodynamics to the Process Industries1 WAYNE C . EDMISTER Foster Wheeler Corporation, New York City
A
LMOST everyone in scientific and industrial circles has a t least some knowledge of thermodynamics and its applications. Mathematician, physicist, chemist, steam power engineer, chemical process engineer have diierent but related understandings. If thoroughly understood and applied with imagination, thermodynamics can be a very useful and powerful tool in process research, development, design, and operation. Although used extensively in the process industries, its powers are not being fully exploited because too few fully appreciate its potentialities and understand the methods of application. During recent years, thermodynamics has been applied to an ever increasing number of process problems. Because of the numerous fluids and operations en-
-
1 Presented jointly l,elorc the Divisions of Chemical IMncation and Physical and Inorganic Chemistry of thc American Chemiral Society, IORth meeting, S e w York City. S ~ p t ~ r n b e11. r 1944.
countered in the process industries, this field of application is almost unlimited. Recent developments in petroleum refining, synthetic rubber, and synthetic chemicals clearly indicate that the chemist and chemical engineer will be dealing with many new constituents and processes in the future. This trend makes the application of thermodynamics even more important. By means of thermodynamics, i t is possible to make the most of research and engineering efforts. The most favorable temperature and pressure conditions for a given chemical reaction and the equilibrium distribution of products may be predicted and thus save considerable laboratory time. Process design calculations can be made by means of phase distribution and heat data correlations and thus avoid excessive pilot plant development work. Exploratory research and pilot plant development work are necessary to determine space velocity, catalyst composition, etc., but the
proper use of thermodynamics will permit making the most of experimental work. TYPES OF APPLICATIONS
There are five types of process applications of thermodynamics, namely: ( 1 ) combustion, including furnaces and regeneration cycles; (2) heat balances, iucluding vaporization, condensation, distillation, and heats of reaction; (3) power, including pumping, compression, steam and electric drives, and flue gas turbines; (4) phase equilibrium for ideal and nonideal solutions; and (5) chemical reaction equilibrium, involving estimation of equilibrium conditions and yields for reactions. In general, the same procedure is followed in each of the above groups of applications. First, experimental data are obtained and correlated. Second, tabulations and charts of derived thermodynamic properties are developed. Third, the correlated experimental and derived thermodynamic properties are applied to the problem. The application of thermodynamics to physical process operations, such as fluid flow, heat transmission, distillation, etc., involves changes in heat or work and phase equilibria for which fugacities, entropies, and enthalpies for liquids and vapors, both pure and in mixture are required. The application of thermodynamics to chemical reactions involves the use of free energies for the reactants and the products, for which heats of fusion, vaporization, and formation as well as heat capacities are required. FUNDAMENTALS OF THERMODYNAMICS
A thorough working knowledge of the fundamentals for most applications and desirable for all others. It is easy to lose sight of the fundamentals while working with the details. Six tables (Tables 1 through 6) have been prepared presenting the fundamentals that constitute the framework of the thermodynamics in the process industries. The equations shown are all derived by applying mathematics to the fundamental concepts and laws. of thermodynamics is
Transformation of Variables. The language of thermodynamics is mathematics. In deriving thermodynamic equations, i t is frequently necessary to transform variables. Table 1shows six relations for making these transformations, which are derived by manipulating general differential equations defining the relationship of the variables. From a knowledge of these transformations it is easy to master the derivation of the thermodynamic relationships. Laws and Concepts. The fundamental laws and concepts of thermodynamics are summarized in Table 2 where the three laws are defined. The first and second laws together form the foundation for most of the thermodynamics used in the process, industries. The concepts of conservation and degradation of energy permit developing many useful equations for thermodynamic properties of fluids and for phase and reaction equilibria. The third law, which enters into the computation of free energies for reactions, has fewer application than the fist two laws. Entropy, the quantitative measure of the degradation or unavailability of energy, is the most frequently misunderstood concept of thermodynamics. The missing link in the understanding of entropy appears to be the significance of the degradation of energy and its relation to the derivation of the various thermodynamic equations. Considerable confusion exists regarding reversible and irreversible processes and the related significance of entropy. The Carnot cycle is a classic means of explaining reversibiity and entropy. Hence, the power and refrigeration Carnot cycles are included in this table of fundamentals. Specific heat and Toule-Thomson relations are also shown to illustrate important fundamental relations derived from the first and second laws. PROPERTIES The thermodynamic properties required for the many fluids handled in the process industries include: densities, vapor pressures, critical state, fugacities, entropies, enthalpies, and free energies. Some of these THERMODYNAMIC
~--FUNDA~ LAWS ~ A AND L CONCEPTS OF THERMOTABLE1-SIX MATHEMATIC TRANSFORMATIONS OF VARIABLES TABLE -Courrcsr
Prof. T. P. Youna. Univnrily ofChicngo
DYNAMICS
THERMO~YNAMIC POTENTIALS TRANSFORMED
TABLE 3-DEPINITIONS
AND
EOUATIONS OP FOURTHBRMO-
properties must be experimentally determined, while others are computed from basic experimental data by means of thermodynamic equations. Themodymmic Potentials. The four thermodynamic potentials (residual work, free energy, internal energy, and enthalpy) are all related to each other as shown by the definitions in Table 3. These four properties are functions of pressure, temperature, volume, and entropy in a systematic manner. The residual work is useful in deriving phase equilibria relations, as is the free energy, the choice depending upon the type of data forming the basis for the computations. Internal energy and the enthalpy are also important functions, the enthalpy being the most frequently and widely used of all four thermodynamic potentials. Experimental Data. The following types of experimental data are required for computing thermodynamic properties: (a) volumetric data, i. e., pressurevolume-temperature measurements, including vapor pressures and critical data; (b) calorimetric data, i. e., specific heats, latent heats of fusion and vaporization, heats of combustion and formation; (c) thermal coefficients, i. e., Joule-Tbomson coefficient and the isothermal effect of pressure on the enthalpy; and ( d ) phase behavior data, i. e., the amounts and composition of the equilibrium liquid and vapor a t various temperatures and pressures. It is important that chemists and chemical engineers working in this field be conversant with previous and current experimental work. Sage and Lacey (12) have made many contributions in this field. Pressure-volume-temperature data for single component hydrocarbon systems are available in sufficient quantity and quality to permit developing adequate correlations. One technique used in obtaining P-V-T data is the calibrated high-pressure glass capillary tube, used by W. B. Kay (7). Although more single component P-V-T data would be of interest, the need for data on mixtures is much more urgent. With more than one component in the system, the P-V-T experimental problem is complicated by the need for composition d a k on the equilibrium vapor and liquid in the two phase region. P-V-I-T data on binary
L
TABLE4--THERMODYNAMIC, G a ~ m c ,AND ANALYTICEQUATIONS OF STATE FOR USE IN C O ~ T T I N G THERMODYNAMIC PROPER TIE^ OF FLUIDS systems also yield phase equilibria information. For three or more components, this method has limitations because the compositions of the equilibrium vapor and liquid cannot be determined. Specific heats of liquids and vapors as well as the heats of vaporization are required in preparing entropy and enthalpy charts. Spectroscopicmethods have been employed extensively in the computation of heat capacities. In this connection, it is felt that there should be more calorimetric data obtained to check the spectroscopic heat capacities. Likewise, more calorimetric data should be obtained to check heats of vaporizations computed from the vapor pressures and the densities of saturated vapor and liquid. The Joule-Thomson coefficient and the isothermal effect of pressure on the enthalpy may be computed from volumetric data. However, these calculated values should also be checked by experimental data, especially for mixtures. Roebuck (11) has made.many contributions of Joule-Thomson coefficientdata. Gilliland, et al. (5, 6 ) has experimentally determined the isothermal effect of pressure on some gases. Equations of State. Graphical and analytical methods are used in correlating P-V-T data for hydrocarbons. Table 4 presents several equations of state. The graphical methods have been used more extensively than the others. In the graphical methods the P-V-T data for pure hydrocarbons are correlated by means of the theorem of corresponding states by using reduced conditions, i. e., ratios of the actual values of pressure, temperature, etc., to the values a t the critical state. One technique employed in computing thermodynamic properties of hydrocarbons graphically is to use the volume residuals, i. e., difference between the perfect gas and the actual volumes. By means of volume residuals, the derivatives of the volume may be evaluated accurately by graphical methods. The P - V - T data for mixtures may be correlated on the same graph with pure components by using the pseudocritical state in computing thc rcduced conditions for the mixture, estimating the pseudocritical for
the mixture from the true criticals of the components. The pseudocritical concept, a contribution of W. B. Kay (7) and a very useful chemical engineering tool, is adequate for estimating densities and changes in enthalpies for hydrocarbon mixtures. Although valuable in these respects, the pseudocritical concept is too approximate for use in developing phase equilibria relationships for mixtures in the higher pressure ranges where the laws of ideal solutions do not apply.
ICf"ir"wur" or w a r cm*w*r*r c " m me r w a Parrs"aE .I. 'Sf*= r w m w PURE eo*-rm I* LIWID vn.Sn
IN Y A W T O N W . , O L
PIME PREIOUR,
AT T*E
P.
SDLY~"" - F"OI"TIE3 I* sm* YsYlD U D ".*I1
L*
cD*s~*rws
4 WHEW
==V+
3.C.*vs.Gcu.L
EQUATION
P.LSIY.E 01 STATE
TABLE &PHASEE ~ ~ L I B E IRELATIONSHIPS UM FOR NONIDEAL SOLUTIONS
'
MTTHW]
IDEAL AND
With reference to the use of reduced states in correlating density data, K. M. Watson (14) recently published a correlation of this kind for liquid densities that is of interest and value to chemical engineers. The equation of state developed by Benedict, et al. (I) forms the basis for deriving accurate relations for computing densities, entropies, enthalpies, free energies, and fugacities for single and multicomponent systems. This equation of state is the most versatile known to the writer. It will be noted that the Benedict equation of state is explicit in pressure, which makes i t difficult to obtain volume derivatives. However, this disadvantage is offset by the fact that this equation applies to both liquid and vapor phases. This is not possible in an equation explicit in volume. The constants for the Benedict equation are evalnated from experimental data, such as vapor pressures, densities, critical conditions, heats of vaporization, etc., for pure hydrocarbons, and then computing the constants for mixtures from the constants for the individual components by the relations shown in Table 4. This equation is particularly useful in preparing tables and charts of thermodynamic properties for use in making routine process calculations. It is not well adapted for direct use in making these routine calculations, however, because of its complexity. This indirect application to the development of tables and charts of thermodynamic properties is one of the most important applications of thermodynamics in the process industry. Phase Equilibrium. For some mixtures, and temperature-pressure conditions, the vapor pressures and
the total pressures may be used in making phase eqnilibrium calculations. In these cases only vapor pressure correlations are required. For other situations where vapor pressures cannot be used but the liquid and vapor phases are ideal solutions, "ideal fugacities" or "corrected vapor pressures" may be used in phase equilibrium calculations. These fugacity equilibrium constants are obtained from the P-V-T data for the pure components, by means of graphical or analytical equations of state. At higher pressures, i. e., near the critical, the liquid and vapor phases are nonideal so the problem becomes much more complicated. Table 5 shows the important features of the thermodynamics relating to these three methods of making phase equilibria calculations. This table shows the equations for the vapor pressure and ideal fugacity phase distribution constants, which are straightforward and require no further explanation. The situation regarding nonideal solutions, on the other hand, is quite different. Several empirical and theoretical attacks have been made on this type of equilibrium problem. From a theoretical standpoint, separate correlations of the fugacities for the liquid and vapor phases (as functions of temperature, pressure, and pbase composition) would be desirable providing the correlations were not too complex. Such fugacities could be computed with relations derived from the Benedict equation of state. The preparation and application of such data are a laborious procedure, however. Experimental phase eqnilibrium data should be used to supplement the equation of state calculations. An empirical method, employing the convergence pressure concept, has been proposed by G. G. Brown. This method, which is discussed in an article by White andBrown (15), is based on the fact that on an equilibrium constant vs. pressure plot for a given constant temperature the lines for different hydrocarbons converge a t a high pressure, which is the critical pressure when the temperature is the critical temperature. Experimental data are required on many mixtures to develop this method, which should prove to be adequate for most ordinary problems and also simpler than the separate fugacity method. The experimental phase equilibria data required in developing the separate fugacity and the convergence pressure correlations may be obtained by determinations of batch or flow pbase equilibria. The high pressure calibrated glass tube used by Kay (2, 7) is an example of the batcb technique. This method is very good for determining border curves and the relative amounts of liquid and vapor. The compositions of the equilibrium vapor and liquid cannot be found with this method. For binary systems, the eqnilibrium constants may be computed from these border curves. For more than two components the equilibrium bomb may be used. In this method, samples of the equilibrium vapor and liquid may be removed for analysis by displacing the volume of the samples with mercury t o maintain equilibrium. Another method employed with success by Gilliland (6) is the equilibrium still method,
which may be called semicontinuous. Continuous phase by means of the more sound equation of state method. equilibria determinations have been made in two types The two methods were found to be in satisfactory agreeof equipment, as illustrated by White and Brown (15) ment a t the points checked. Charts of this kind are useful in making refrigeration calculations, which often and by this author ( 4 ) . For some multicomponent higher-boiling petroleum arise in the process industries. Hydrocarbons, both fractions, such as gasoline, the component technique of pure and in mixtures, are frequently used as refrigermaking phase equilibria calculations is not practical ants. In this connection, the method of York (17) for because of the large number of components. For mix- making compression calculations is useful where i t is tures of this type, it is necessary to use empirical meth- not practical to prepare Mollier diagrams for the fluid ods based on laboratory distillations to construct the in advance. Enthalpy vs. temperature charts for higher-boiling phase diagram, from which the boiling points, dew points, and relative amounts of liquid and vapor may petroleum fractions, such as gasoline, etc., can be prebe obtained. Likewise, empirical correlations can be pared by using the pseudocritical technique with derived to estimate the composition of the equilibrium graphically integrated volumetric derivatives. On charts of this kind the constant pressure lines slope in vapor and liquid. Phase diagrams for three petroleum fractions were the two-phase region, representing the change in tempublished recently ( 4 ) from data obtained by continu- perature between the boiling and dew lines, which ous equilibrium flash vaporization runs a t different bound the two-phase region forming the phase diagram. temperatures and pressures. It is of interest to note Thus charts of this kind are a combination phase and that the lines of constant per cent vaporized are enthalpy diagram and very valuable in making compustraight lines on log of the pressure to the base 10 vs. tations for the mixture. For example, the final temreciprocal of absolute temperature. The lower portions perature after throttling a t constant enthalpy into or out of the two-phase region may be found from this of these lines can be predicted by ideal fugadties. Entropies and Enthalpies. The preparation and the chart. Chemical Reaction Equilibrium. Thermodynamics application of entropy and enthalpy charts and tabulations for pure fluids and their mixtures represent one may be used to estimate the equilibriulil of a given reof the most important applications of thermodynamics. action and thus predict the conditions most favorable In computing entropies and enthalpies for these charts to it. By a combination of thermodynamics and kiand tables, it is customary to correlate, smooth, inter- netics, the equilibrium distribution of products may be polate, and extrapolate the experimental vapor pres- estimated. The heat absorbed or liberated in a reaction sure, heat capacity, latent heat, and volumetric data may also be found by means of equations derived by by graphical or analytical methods. thermodynamics. The fundamental equations for The isobaric effects of temperature on the entropy or these computations are given in Table 6. the enthalpy are computed from the heat capacity, while the isothermal effect of pressure may be computed from volumetric data by means of thermodynamic equations. As indicated above, i t is desirable but not always uecessary to have experimental data on the effect of pressure also. Graphical methods using residual volumes have been applied to pure components by several workers (3, 16, 18) in this field. This method may also be applied to mixtures by means of the pseudocritical concept. Another method that has been applied to single and multicomponent systems is the equation of state of Benedict. This method is more tedious than the pseudocritical technique for mixtures but on the other hand is theoretically sounder. Enthalpy vs. temperature charts for the lighter hydrocarbons can be prepared from existing data. These charts can be applied to mixtures by assuming that the enthalpies are additive. The accuracy of heat balances made by the writer on light hydrocarbon process equipExperience a t many research laboratories has proved ment indicates that the assumption of additivity is the value of compiling tabulations and charts giving justified for these hydrocarbons a t moderate pressures. thermodynamic data for the formation of various comMollier diagrams, i. e., charts involving entropy and pounds of interest to that organization. For example, enthalpy for light hydrocarbons and some of their petroleum research laboratories have done this for the mixtures, have been prepared and published ( 8 ) . These heats and free energies of formation for the hydrocarcharts were prepared by the graphical method, assum- bons. These data are computed from heats of formaing additivity for the mixtures, and then spot checked tion and entropies, the latter being prepared by means
of the third law and low-temperature heat capacities as deiined by hydrogen/carbon ratio of the fuel and together with heats of vaporization and fusion. Heats excess oxygen. Process Operations. Thermodynamics plays an imand free energies for reactions are found by combining the heats and free energies of formation for the react- portant role in the design and operation of commercial processes. Recent process developments in the peants and products. Although thermodynamics is very useful in studying troleum industry have resulted in great progress along chemical reactions, it does not give any clue to the ap- synthetic lines. In addition to motor fuel and lnbriproach to equilibrium. For this, supplementary data cants, special hydrocarbons are now being manufacon heat transfer rates, diffusion coefficients, rates of tured for inclusion in aviation gasoline and for the mixing, viscosities, and reaction velocities are required. manufacture of explosives. In addition, various alExploratory research and pilot plant development work cohols and raw material for manufacture of synthetic are necessary to obtain this supplementary information. rubber and plastics are prepared from petroleum hydrocarbons. A recent article by Murphree (9) describes many new developments in the petroleum industry. PROCESS APPLICATIONS Many chemical processes are in operation and others Practically all industrial processes involve the con- are being developed to manufacture products essential version of energy from one form to another and of to war and peace activities from different starting raw course some energy is always lost to the low-tempera- materials, such as: natural gas, refinery gases, casingture heat "sink," which may be the flue gas stack, the head gasoline, petroleum, coal, shale, salt, corn, wheat, corn cobs, rice hulls, sawdust, etc. All of these proccooling water, etc. Unit Operations. In the design and operation of esses have many similarities. Regardless of future dechemical processes, the chemical engineer is concerned velopments the process industries will still be concerned with the unit operations, namely: fluid flow, heat trans- with the same fundamentals and unit operations. Withfer, vaporization and condensation, absorption and out going into detail, a few of the thermodynamic apstripping, distillation and extraction, combustion and plications will be discussed. The recent development and commercialization of catalyst regeneration, etc. In all of these unit operations, thermodynamics is a useful tool. In the flow of the fluid catalyst cracking process has started a new fluids, various forms of energy are involved. In the trend in catalysis. In this process fine mesh catalyst is transfer of heat, enthalpy is the contribution of ther- fluidized by steam, air, or hydrocarbon vapors and cirmodynamics. For the separation processes, phase culated through the reaction and regeneration stages equilibria and enthalpy data are required in making the of the process. This principle has been applied to the various design calculations and analyzing plant per- cracking of petroleum to produce high-octane aviation gasoline. In the future i t will undoubtedly be applied formance. Where there are substantial variations in the mold to other process operations as well. The fluidized cataoverflow in distillation and extraction operations it is lyst presents many problems, some of which can he necessary to make heat balance calculations a t fre- solved by the use of thermodynamics. Although the quent intervals. For these calculations constant pres- fluid catalyst principle is new its application involves sure plots of enthalpy vs. compositions with constant the use of various well-known unit operations, such as temperature tie-lines are sometimes helpful. Recent heat transfer, distillation, etc., to prepare the feed articles by Randall and Longtin (10) and an earlier one stock and handle the products from the reaction. In contrast to the fluid process there are many new by Thiele (13) deal with this technique. In most processes, preheating and vaporization fur- processes in operation employing a stationary catalyst naces are required to prepare the fluid for reaction. bed with intermittent reaction and regeneration. An The design of these furnaces is usually more compli- example of this type of process in the petroleum incated than the design of steam boilers because of the dustry is the hydroforming process for the manufacture type of fluid being handled, it being necessary to con- of aromatics. In the commercial version of this procsider the time-temperature gradient for the fluid in ess, there are usually two sets of reactors so that one is order to avoid overheating and thermal decomposition. reacting while the other one is being regenerated. The The combustion and flue gas calculations, which are no regeneration of the catalyst is accomplished by the cirditferent from those for steam boilers, require heats of culation of flue gas containing oxygen, the amount of combustion and specific heats of the combustion prod- oxygen being regulated to permit regeneration without ucts. In many proctss furnaces, flue gases are recircu- o~erhcatingtbe~atalyst.The heat jibcrated by bumlatecl to avoid overheating and a t the same time keep ing the catalyst deposit is removed in waste heat boilers the economy as high as possible. generating steam, the excess flue gas produced being There are a number of other operations where flue removed from the system by venting the gases to the gas calculations must be made, namely, catalyst re- atmosphere through a flue gas turbine generating bygeneration cycles, waste heat boilers, and flue gas tur- product power to compress the flue gases and the air. bines. For these calculations it is necessary to have Another example of the intermittent catalytic proctables and charts of volumes, entropies, and enthalpies, ess is the Houdry Process, where oil is cracked in staas functions of pressure, temperature, and composition, tionary catalyst beds that are also regenerated inter-
mittently. The gas from regeneration of the catalyst is likewise expanded through a flue gas turbine, thus generating power for the compression of air for regeneration. In this process the temperatures in the reaction and regeneration zones are controlled by means of a circulating molten salt, which carries heat from a regenerating to a reacting catalyst bed. A very important consideration in the design and operation of every process is the over-all heat balance, i. e., the balance between the various power and heating loads. Power for pumping and compressing might be supplied by electricity, steam, or gas engines. Process and building heating is usually supplied by steam a t different pressures, depending upon the duty. It is important that this balance be worked out for greatest economy through all seasons of the year. If there are uncertainties in the process heating and power requirements, the utilities may not be properly designed, with the result that i t may be necessary to blow steam to the atmosphere in the summer or cool excessive amounts of high pressure steam in the winter to maintain a heat balance on the operation. Accurate thermodynamic properties of the fluids being processed are obviously important for calculation of over-all heat balances. CONCLUSIONS
In conclusion, the science and art of mastering and applying thermodynamics may be divided into the following steps: (1) mathematics; (2) concepts and theories; (3) derived thermodynamic equations; (4) fundamental volumetric and calorimetric data; (5) correlation of data and development of tables and charts of thermodynamic properties; and (6) the a p plication of the above to the problem. It is important that the chemist and chemical engineer have a thorough understanding and familiarity
with the mathematics, laws, and formulations of thermodynamics and that they appreciate but do not overrate its potentialities. In addition, they should have imagination and curiosity regarding the application of thermodynamics to industrial problems and be conversant with the developments and writings of previous and contemporary workers in this field. As in any other subject, i t is of value to be able to discuss thermodynamics intelligently with industrial executives. Chemists and chemical engineers preparing for work in the process industries should receive a sound and inspirational training in thermodynamics and its past, present, and potential applications. LITERATURE CITED
(1) BENEDICT, M., G. B. WEBB,AND L. C. RUBM,Jourml of Chem. Phys., 8, 334-5 (1940); 10, 747-58 (1942). W.H. AND W. B. KAY,Id. Eng. Chem. 24, 291 (2) B$?,"F,
GI~LILAND. E.
R.
AND
R. V.
iu~~s,'~nd.'Eng. Chem., 32,
17 (1940).
.EAND, E. R. AND H. W. SCHEELINE, ibid., 32,48 (1940); (1939). B.. Ind. Eng. Chem., 28, 1014 (1936).
jo
~ N DW. C. EDMISTER, O i l Gar J., 39, 35 (Sept. 4. 1941). MURPHREE, E. V., Ind. Eng. Chem, 35,623 (1943). RANDALL, M. AND B. LONGTIN, Ind. Eng. Chem., 30, 1063.
1188 (1938); 31, 1191 (1939). AND H. OSTERBERG, Phys Rev., 45, 332 (1934); 46,785 (1934); 48,450 (1935). SAGE, B. H. AND W. N. LACEY, "Volumetric and Phase Be-
ROEB~CK. J. R.
havior of Hydrocarbons." Stanford University Press, Stanford University, 1939. THIELE, E. W., I d . Eng. Chem., 27,392 (1935). WATSON, K. M.. ibid.. 35.398 (1943). WHITE,R. R. A . i2 (1942) YORK,R., ibid., 32, 54 (1940). Yo=, R., aid.,34, 535 (1942). YORE,R. AND H. C. WEBER,ibid., 32,388 (1940).
(The lost *per in this symposium
The expiration date for the salts of penicillin, originally 90 days, has been extended considerably following intensive stability investigations, and i t has now been definitely established that there is no loss of potency after some 350 days when the sodium salt is stored a t -5"C., said Peter P. Regna, of the Chas. P6zer & Co., Research Laboratories, Brooklyn, in a paper read before the meeting of the American Institute of Chemical Engineers held in St. Louis. Dr. Regna said i t was fortunate that the salts of penicillin, sodium and calcium, are so stable, otherwise the problem of transportation to and storage of penicillin in the various battle areas would present insurmountable difficulties. He described the steps necessary to provide the remarkable new antibiotic substance in billions of units to the armed forces and civilian hospitals. Much of the process has to be carried out a t very low temperatures, and at some intermediate stages it has to be hurried, as during the adsorption treatment with moist
carbon, when its stability exceeds only a few hours. Penicillin, he said, is biologically inactivated by high temperatures, by acids and bases, moisture, heavy metals, primary alcohols, and by oxidizing agents. Penicillin also is rapidly destroyed by an enzyme from bacteria called "penicillinase." These and other contaminants, therefore, must be rigorously excluded, and these conditions impose a marked limitation upon the techniques which may be employed for the recovery of the chemo-therapeutic agent. Following initial fermentation in deep tanks under sterile conditions, penicillin undergoes a number of steps involving the use of solvents, adsorption on activated carbon, filtration, drying. After it has been re-extracted from one of the solvents with dilute sodium bicarbonate, it may be safely handled thrdugh all subsequent steps, said Dr. Regna, right to its enclosure in the final container without signs of inactivation. In serum bottles sterilized penicillin can then be stored a t least a year without any effects on its potency.
